CO₂ in Flowing Freshwater: What can we learn from 30-Years of Data?

Presenting the data pipeline and workflow for the compilation of CDFLOW.

Abstract

Carbon dioxide (CO₂) concentrations in the atmosphere have been steadily increasing since the mid-twentieth century. This rise in CO₂ has been shown to affect a wide range of ecosystems and organisms, with a number of negative effects of elevated CO₂ documented for marine organisms. Less is known about the dynamics of CO₂ in freshwaters (referred to as the partial pressure of CO₂, pCO₂), but the potential exists for freshwater organisms to be challenged by elevated pCO₂. Direct measures of pCO₂ in freshwater are limited making it challenging to define spatial or temporal trends. However, pCO₂ can be estimated from pH, temperature, and alkalinity—commonly collected water quality metrics. We used the National Water Quality Monitoring Council data portal as a source of water quality metrics and the program PHREEQC to estimate pCO₂ in flowing freshwaters across 35,000 sites spanning the lower 48 US states (CONUS) from 1990 through 2020. Site data for water chemistry measurements were spatially joined with the National Hydrology Dataset to define sites. Using CDFLOW data we modeled spatiotemporal pCO₂ trends in flowing freshwaters from 1990 through 2020 across the CONUS using linear mixed models. CDFLOW presents an opportunity for spatiotemporal analysis of pCO₂ in flowing freshwaters. However, CDFLOW also presents an opportunity for researchers to add pCO₂ to their datasets for further investigation when modeling.